Risk Of Cascading Failures Research Articles

Repair strategies for minimising the risk of cascading failures in electricity networks

In this work, we develop repair strategies for simplified models of electric power grids. The goal is to gain insight into the combinatorial properties of repair problems in order to improve maintenance and restoration planning. Firstly, we consider a seriously damaged grid and try to find the set of lines that should be repaired first in order to resupply the customers as fast as possible. We analyse two abstract repair problems that are also of theoretical interest and show how to solve them approximately. Secondly, we consider a power grid during normal operation where only a few lines are not operating due to random failures. We try to find repair strategies that minimise the risk of cascading failures in such situations. We develop a blackout model in order to understand the dynamics of blackouts and propose a repair strategy. The first computational results indicate that the proposed strategy provides a good starting point for the development of further repair strategies.

Complex systems analysis of series of blackouts: Cascading failure, critical points, and self-organization

We give an overview of a complex systems approach to large blackouts of electric power transmission systems caused by cascading failure. Instead of looking at the details of particular blackouts, we study the statistics and dynamics of series of blackouts with approximate global models. Blackout data from several countries suggest that the frequency of large blackouts is governed by a power law. The power law makes the risk of large blackouts consequential and is consistent with the power system being a complex system designed and operated near a critical point. Power system overall loading or stress relative to operating limits is a key factor affecting the risk of cascading failure. Power system blackout models and abstract models of cascading failure show critical points with power law behavior as load is increased. To explain why the power system is operated near these critical points and inspired by concepts from self-organized criticality, we suggest that power system operating margins evolve slowly to near a critical point and confirm this idea using a power system model. The slow evolution of the power system is driven by a steady increase in electric loading, economic pressures to maximize the use of the grid, and the engineering responses to blackouts that upgrade the system. Mitigation of blackout risk should account for dynamical effects in complex self-organized critical systems. For example, some methods of suppressing small blackouts could ultimately increase the risk of large blackouts.

Risk assessment of catastrophic failures in electric power systems

The declining reliability of the US electric power system is raising major concerns among both politicians and power engineers in the USA. One of the reasons put forward by the North Electric Reliability Council (NERC) is the detrimental role played by the protection systems during large disturbances, which tend to help the perturbations to propagate through over-tripping of fault free system components due to hidden failures. It turns out that the present practice in power transmission planning and online security analysis is to neglect the impact of the protection systems. In addition, the aim is to mitigate the vulnerability of the system to the loss of a single piece of equipment only by carrying out an N-1 security analysis. Consequently, the risk of cascading failures leading to blackouts and brownouts is neither assessed nor managed. This paper describes methodologies together with algorithms that assess the conditional risk of catastrophic failures in electric power networks due to hidden failures in protection systems. A catastrophic failure, defined as one that results in the outage of a sizable amount of load, may be caused by dynamic instabilities in the system or exhaustion of the reserves in transmission due to a sequence of line tripping leading to voltage collapse. Only the latter case is being considered. The aim of these algorithms is to identify the weak links in the systems, which are defined as those branches of the network whose tripping due to a fault lead to the highest probabilities of a catastrophic failure. The proposed methods are demonstrated on a 7-bus and a 61-bus system.